1. Field of the Invention
The present invention relates to a digital signal decoding circuit used for discriminating a code of a received digital signal in, e.g., a digital radio communication system.
2. Description of the Related Art
In a digital radio communication system, a transmission station converts codes of a digital signal, i.e., "1" and "0" into a change in frequency or voltage value, and transmits the signal. A reception station receives and demodulates a signal sent from the , transmission side, and compares the received digital signal with a signal level of a reference signal to discriminate the codes ("1" and "0").
A conventional decoding circuit of this type has the following problems. More specifically, a reference signal level is fixed in advance to a predetermined value. For example, assume that a variation in modulation/demodulation frequency or a variation in voltage value occurs in a transmission or reception station, and a DC level of a received digital signal is changed. In this case, accurate code discrimination cannot be performed, and as a result, a decoded output includes an error.